The increasing cost of fossil fuel and environmental concerns have stimulated worldwide interest in developing alternatives to petroleum-based fuels, chemicals, and other products. Biomass materials are a possible renewable alternative.
Lignocellulosic biomass includes three major components. Cellulose, a primary sugar source for bioconversion processes, includes high molecular weight polymers formed of tightly linked glucose monomers. Hemicellulose, a secondary sugar source, includes shorter polymers formed of various sugars. Lignin includes phenylpropanoic acid moieties polymerized in a complex three dimensional structure. The resulting composition of lignocellulosic biomass is roughly 40-50% cellulose, 20-25% hemicellulose, and 25-35% lignin, by weight percent.
No cost-effective process currently exists for efficiently converting cellulose, hemicellulose, and lignin to components better suited for producing fuels, chemicals, and other products. This is generally because each of the lignin, cellulose and hemicellulose components demand distinct processing conditions, such as temperature, pressure, catalysts, reaction time, etc., in order to effectively break apart its polymer structure.
One can use expensive organic solvents such as acetone, ethanol, 4-methyl-2-pentanone, and solvent mixtures, to fractionate lignocellulosic biomass into cellulose, hemicellulose, and lignin streams (Paszner 1984; Muurinen 2000; and Bozell 1998). Using this process, the organic solvents dissolve some of the lignin such that it is possible to separate the dissolved lignin from the solid cellulose and hemicellulose. To the extent that the lignin can be separated, it can be burned for energy or can be converted with a ZSM-5 catalyst to liquid fuel compounds, such as benzene, toluene, and xylene (Thring 2000).
After removing the lignin from biomass, one can depolymerize the delignified lignocellulose by acid catalytic hydrolysis using acids such as sulfuric acid, phosphoric acid, and organic acids. Acid catalytic hydrolysis produces a hydrolysate product containing sugars, acid, and other components such as polyols, oligosaccharides, organic acids, lignin, and proteins. The hydrolysates can be separated using known fractionation processes. One can alternatively employ a specialized acid catalytic hydrolysis technology developed by Arkenol, Inc. to convert cellulose and hemicellulose in biomass to sugars using highly concentrated acid and to separate sugars from acid using a simulated moving bed process (Farone 1996).
Cellulose and hemicellulose can be used as feedstock for various bioreforming processes, including aqueous phase reforming (APR) and hydrodeoxygenation (HDO)—catalytic reforming processes that, when integrated with hydrogenation, can convert cellulose and hemicellulose into hydrogen and hydrocarbons, including liquid fuels and other chemical products. APR and HDO methods and techniques are described in U.S. Pat. Nos. 6,699,457; 6,964,757; 6,964,758; and 7,618,612 (all to Cortright et al., and entitled “Low-Temperature Hydrogen Production from Oxygenated Hydrocarbons”); U.S. Pat. No. 6,953,873 (to Cortright et al., and entitled “Low-Temperature Hydrocarbon Production from Oxygenated Hydrocarbons”); and U.S. Pat. Nos. 7,767,867 and 7,989,664 and U.S. Application Ser. No. 2011/0306804 (all to Cortright, and entitled “Methods and Systems for Generating Polyols”). Various APR and HDO methods and techniques are described in U.S. Patent Application Ser. Nos. 2008/0216391; 2008/0300434; and 2008/0300435 (all to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); U.S. Patent Application Ser. No. 2009/0211942 (to Cortright, and entitled “Catalysts and Methods for Reforming Oxygenated Compounds”); U.S. Patent Application Ser. No. 2010/0076233 (to Cortright et al., and entitled “Synthesis of Liquid Fuels from Biomass”); International Patent Application No. PCT/US2008/056330 (to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); and commonly owned co-pending International Patent Application No. PCT/US2006/048030 (to Cortright et al., and entitled “Catalyst and Methods for Reforming Oxygenated Compounds”), all of which are incorporated herein by reference.
Biomass must be deconstructed to less complex oxygenated compounds prior to use as feedstock for bioreforming processes. There remains a need for cost-effective methods for separating biomass into streams suitable for use in APR, HDO and other bioreforming processes: